1. Field of the Invention
This invention relates to a color image recording system, and more particularly to a color image recording system in which occurrence of color displacement is prevented.
2. Description of the Related Art
As disclosed, for instance, in Japanese Unexamined Patent Publication No. 3(1991)-41871, there has been known a color image recording system in which three color beams are respectively modulated according to an image signal and caused to scan a photosensitive material, thereby recording a color image on the photosensitive material.
In such a color image recording system, the three color light beams are combined together and caused to scan the photosensitive material so that they simultaneously impinge upon the same point on the photosensitive material for each pixel, or caused to scan the photosensitive material so that they impinge upon the same point on the photosensitive material for each pixel one after another. In either case, the three color light beams modulated according to an image signal component for each pixel should impinge upon the photosensitive material at the same point for each pixel. However for various reasons including electrical and optical reasons, the three color light beams cannot impinge upon the photosensitive material accurately at the same point, which causes color displacement in the recorded color image.
In Japanese Patent Publication No. 5(1993)-29188, there is disclosed a color image recording system in which occurrence of color displacement is prevented. The color image recording system is one in which the three color light beams are caused to scan the photosensitive material one after another. In the color image recording system, a single photodetector which detects all the three color beams is provided, and recording by the three (first to third) color beams are initiated predetermined times t1, t2 and t3 after detection of the first to third color beams, respectively.
In the color image recording system, by properly setting the predetermined times t1, t2 and t3, the recording start points of the first to third color beams can be properly adjusted, whereby occurrence of color displacement can be prevented.
However in the arrangement described above, since all the color beams, e.g., R (red), G (green) and B (blue) beams, are detected by a single photodetector, there is required a complicated circuit for separating a detecting pulse for each color beam from a signal in which detecting pulses for the three colors are mixed. Since the intensities of the three color beams greatly differ from each other, the circuit must be wide in the detecting range.
This problem is due to spectral sensitivities of the color photosensitive material and the photodetector. That is, as shown in FIG. 6, the sensitivity of a typical color photosensitive material to R, G and B light beams increases in this order and accordingly the intensities of the recording light beams for a given density should be set to decrease in this order. Further the sensitivity of a typical photodetector such as of silicon decreases in this order as shown in FIG. 7 and accordingly the detecting signal output from the photodetector for a given intensity of the light is at a higher level for a R light beam and is at a lower level for a B light beam.